1. Field
One or more exemplary embodiments relate to a tomography apparatus and a method for reconstructing a tomography image by the tomography apparatus.
More specifically, one or more exemplary embodiments relate to a tomography apparatus that constructs a tomography image by performing a tomography scan on a moving object, and a method for reconstructing a tomography image which is performable by the tomography apparatus.
2. Description of the Related Art
Medical imaging apparatuses are equipment configured for acquiring an internal structure of an object as an image. Medical image processing apparatuses are noninvasive examination apparatuses that capture images of the structural details of a human body, internal tissue thereof, and fluid flow within a human body, process the images, and show the processed images. A user such as a doctor may diagnose a health state and a disease of a patient by using a medical image output from a medical image processing apparatus.
Representative examples of apparatuses for radiating X-rays onto a patient to scan an object include tomography apparatuses. Examples of the tomography apparatuses include a computed tomography (CT) apparatus.
Among medical image processing apparatuses, CT apparatuses are capable of providing a cross-sectional image of an object and distinctively expressing inner structures (e.g., organs such as a kidney, a lung, etc.) of the object, as compared with general X-ray apparatuses. Thus, CT apparatuses are widely used for accurately diagnosing a disease. Hereinafter, a medical image acquired by a tomography apparatus is referred to as a tomography image. In detail, a medical image acquired by a CT apparatus is referred to as a CT image.
To acquire a tomography image, a tomography scan is performed on an object using a tomography apparatus, and thus raw data is acquired. The tomography image is reconstructed using the acquired raw data. The raw data may be projection data acquired by projecting X-rays to the object, or a sinogram that is a collection of pieces of the projection data.
For example, in order to acquire a CT image, image reconstruction should be performed using a sinogram acquired by a CT scan. Reconstruction of a CT image will now be described in detail with reference to FIG. 1.
FIGS. 1A and 1B are a schematic diagram and images which illustrate a CT scan and reconstruction of a CT image, respectively.
In detail, FIG. 1A is a schematic diagram which illustrates a CT scan that is performed by a CT apparatus that performs a CT scan while rotating around an object 25 and acquires raw data which corresponds to the CT scan. FIG. 1B illustrates a sinogram acquired by a CT scan and a reconstructed CT image.
The CT apparatus generates X-rays, radiates the X-rays toward the object 25, and detects X-rays that have passed through the object 25 by using an X-ray detector (not shown). The X-ray detector produces raw data which corresponds to the detected X-rays.
In detail, referring to FIG. 1A, an X-ray generator 20 included in the CT apparatus radiates X-rays toward the object 25. When the CT apparatus performs a CT scan, the X-ray generator 20 rotates around the object 25 and acquires a plurality of pieces of raw data, for example, first raw data 30, second raw data 31, and third raw data 32, corresponding to angles to which the X-ray generator 20 rotates, respectively. In detail, the X-ray detector (not shown) detects X-rays applied to the object 25 at a position P1 to thereby acquire the first raw data 30, and detects X-rays applied to the object 25 at a position P2 to thereby acquire the second raw data 31. The X-ray detector (not shown) detects X-rays applied to the object 25 at a position P3 to thereby acquire the third raw data 32. The raw data may include projection data.
In order to generate one cross-sectional CT image, the X-ray generator 20 should perform a CT scan while rotating at least 180° with respect to the object.
Referring to FIG. 1B, a single sinogram 40 may be acquired by combining the first, second, and third raw data 30, 31, and 32 acquired while the X-ray generator 20 is moving at intervals of a predetermined angle as described above with reference to FIG. 1A. The sinogram 40 is acquired via a CT scan performed while the X-ray generator 20 rotates during one cycle. The sinogram 40 corresponding to one cyclic rotation may be used for generation of one cross-sectional CT image. One cyclic rotation may be about more than a half turn or one full turn, according to the specifications of a CT system.
A CT image 50 is reconstructed by performing back-projection with respect to the sinogram 40.
In general, it takes about 0.2 seconds for the X-ray generator 20 to rotate a half turn.
When an object that is a target of a CT scan moves at a relatively fast speed, motion of the object occurs during one cycle. Due to the motion of the object, motion artifacts may occur in the reconstruction of a CT image.
A three-dimensional (3D) CT image may be reconstructed from a plurality of cross-sectional CT images. Thus, while raw data necessary for reconstructing a 3D CT image is being acquired, motion of an object occurs more frequently.
When motion artifacts are present in the reconstructed CT image, an edge of an object may be blurred, or an image may be unclear. The motion artifacts in a CT image degrade the quality of the CT image, and thus when a user, for example, a medical doctor, reads the CT image and diagnoses a disease, the user is unable to accurately read the CT image and diagnose the disease.
Thus, when a CT scan is performed on a moving object, it is important to reconstruct a CT image in which image blurring caused by motion artifacts is reduced.